Fundamental studies on radiation chemistry in liquid phase using 85Kr source

A β-irradiation apparatus using unsealed 85Kr gas as an internal source has been devised for chemical reactions in liquid phase. Studies have been made of its dosimetry, the polymerization of aqueous acrylamide, and the removal of the dissolved 85Kr after irradiation. Experiments were made in a reaction vessel of 1/capacity with 300 Ci of 85Kr. Some of the results obtained are as follows. (1) The dose rate measured by the methylene blue dosimeter agrees relatively well with the theoretical value obtained on the basis of the input charge method. The maximum dose rate reaches 1.8 x 104rad/h. (2) The experimental results for the polymerization by the 85Kr source were compared with the results using γ-rays from a 137Cs source. No difference is observed in the polymerization rates and the degrees of polymerization, while a slight difference is observed in the molecular weight distribution. (3) The removal is accomplished by the combined use of freeze-pump-thaw cycles, N2-stripping and standing at room temperature. The overall decontamination factor reaches 108 and the radioactive concentration of the 85Kr gas dissolved in liquid reactants diminishes to a level below the permissible level. From these results, it should be quite practical to use 85Kr gas as a radiation source for chemical reactions in liquid phase. (auth.)